I wonder if the basal metabolic rates are based on data, or some dumb linear extrapolation that someone did based on college kids in 1969. There's no way they'd still be using that for overweight people, I'm going to assume.

I did a crash diet this past fall and lost about 30 lbs in maybe a little over 2 months only to gain back just over 20 of those lbs since December. Now I'm dieting again but not so extremely as before (which was no breakfast, and a handful of almonds for lunch and one felafel sandwich for dinner during weekdays, weekends I ate more or less what I wanted to).

Slowing of metabolism is an impressive survival mechanism in times of food scarcity. But what I've never understood is what is lost when this mechanism is triggered? Are strength or endurance compromised when metabolism is slowed? I.e. what is the benefit to the human organism of having the faster baseline metabolism during normal times of food availability?

9: I have considered going on an extreme (yet healthy) grocery-budget diet to see what would happen. I imagine the shocking result would be that I'd become constantly hungry and bitchy, and less productive. But I do spend a fortune on food, so it might still be worth it.

I've had pretty large pregnancy-related swings over the past six years, and mostly it has driven home the point of how you can only nudge the needle a teeny bit. Or how I can. Since I stopped nursing for the last time, my appetite has plummeted. It's dramatic.

I actually think that it's not nursing, but the hormone replacement therapy post-hysterectomy. I have a secret theory that my estrogen levels had dropped over all the pregnancies and now they're artificially up to my 20s levels.

I feel like I've left this comment before, which is strange, but I don't actually mind feeling hungry, even quite hungry, if I can focus all my attention on obtaining food. E.g., if I'm hiking and out of food, and won't be able to eat anything until I'm back at camp, walking back to camp is not unpleasant, even if I'm quite hungry. Or if I'm planning to catch and eat fish for dinner, and I'm having a hard time of it, but I can just keep trying. (Or even if I eventually give up and go to bed hungry, planning to try again in the morning.) None of those bother me much. I'm sure it would start to bother me if I ever had to go without food for an extended period, but I've never been in that situation.

But, if I'm hungry and anyone expects me to do anything at all other than figure out when/where/how I'm going to get some food, that's very unpleasant.

Also if I'm very hungry and don't have anything to eat, and you're around me eating food that smells good, I will literally be tempted to kill you and take your food. It's a temptation I will probably resist, but it's a real temptation.

Researchers have discovered a phenomenon called "metabolic compensation," whereby, as people either expend more energy through physical activity or lose weight, their basal metabolic rate slows down.

"The more you stress your body, we think there are changes physiologically -- compensatory mechanisms that change given the level of exercise you're pushing yourself at," said Loyola University exercise physiologist Lara Dugas. In other words, our bodies may actively fight our efforts to lose weight.

What I find most amazing about this is that this implies there are 600 calories per day of efficiency gains to be had. In other words, their body was so inefficient that it can burn 600 calories per day less and still function normally. I would have thought that would be a no go evolutionarily.

Like heebie, I'd like to see the details on how the calculated the expected basal metabolic rate for these folks both before and after.

From the paper: "The predicted RMR [resting metabolic rate] was obtained using a linear regression equation developed using baseline data on body composition, age, and sex in the full 16-person cohort"

So they used a small sample of morbidly obese people to develop their regression, then found that after they lost a bunch of weight their RMR deviated from that regression.

26: How could they have obtained a regression to predict RMR for the cohort based on RMR data for that same cohort? I may be misreading you, but that sounds to me like there was another dataset somewhere correlating RMR with those factors, and they plugged in the cohort's factors against the relevant coefficients.

"Contrary to expectations, the degree of metabolic adaptation at the end of the competition was not associated with weight regain, but those with greater long-term weight loss also had greater ongoing metabolic slowing."

Hm. This effect seems to have been known for a long time (since at least 1990). One older explanation for the phenomenon is that the regression coefficients for fat-free mass and fat mass are mis-estimated because they compensate. Specifically, fat mass burns more calories per kg than the authors regression estimated, mostly because fat-free mass in obese individuals burns less calories per kg than in lean individuals. So the loss of all that fat mass, which is actually burning more calories than the authors think, causes a big drop in metabolic rate.

They took the original obese people and developed a model for their metabolic rate based age, sex, fat-free mass, and fat mass. Then they remeasured those things after they lost the weight, and once more 6 years later after many had gained the weight back. The model said they should have much larger metabolic rates than they actually had at both subsequent points.

They aren't strictly self-comparisons because the model is based on the whole group and the ratio of fat-free mass and fat mass had changed. They didn't publish self-comparisons.

Of the 14 people, 4 basically regained all the weight, and 9 kept off a substantial proportion (roughly half). One went on to lose more weight.

If the model is off, and underestimates the amount of energy that fat mass burns, it would explain some (but not all) of the discrepancy.

I know that BMR isn't a useful number for me. I've not been actively dieting recently, but every time I do, I need to go many hundreds of kcal per day under my predicted BMR to even begin to lose weight. That's not under BMR + a calculated extra intake for activity level, but under BMR simpliciter. I've always assumed that that is a by product of the thyroid.

I had a thyroid tumour about 9 years ago, and have struggled much more than I used to to keep weight off, even though I am prescribed thyroid medication. Pre-thyroid tumour, my stable weight was about 40lbs lower than my current stable weight, and I always found it relatively easy to lose weight via cutting food intake somewhat, or increasing activity somewhat. I wasn't skinny, and my weight fluctuated a bit, but dropping it whenever it crept too high wasn't that hard. These days, I lead a more sedentary lifestyle -- long car commute, versus previously a bike/walk commute -- but there definitely seems to be a core metabolic change, too.

I have a family reunion at the end of the month. It's probably wiser to just tell myself that no matter what I do, I'm going to look hideous next to my selfie-curating elite-college cousins in their late teens and early 20s, but a crash diet sounds awfully appealing. (I don't know how it would work and have never tried. I've long thought I sort of broke my metabolism with eight years of anorexia and then after I had my gall bladder out I really gained. But I think that's mostly making excuses for being older and sedentary and not eating well enough because it seems like so much work.)